It is often necessary for the transmission of the final drive to have an extremely large inter-axial or axle offset between input and output shaft, in order to allow the sprocket wheel of a tracked vehicle to extend as far as possible from the frame or the pan or to allow heavy motor vehicles to have as much clearance from the ground as possible (portal axles).
Furthermore relatively large step-down ratios have to be accommodated within a very confined space, taking into consideration the specific conditions of a final drive.
A final drive for a heavy motor vehicle is known from German Patent document No. 24 18 810, in which a hollow wheel is connected with the output shaft and a driving pinion drives this hollow wheel directly as well as indirectly via intermediate gears. With this arrangement two times two intermediate gears are arranged between pinion and hollow wheel, each set being arranged symmetrically to the pinion and hollow wheel in such a way as to achieve load distribution on the indirect drive of the hollow wheel.
The design scope of gear transmissions of this kind is very limited because of the axle offset and transmission ratio parameters, both of which largely dependent upon one another. The size of the hollow wheel is limited by the specific conditions of a final drive (e.g. by the size of the sprocket wheel drum), and there is a limit to the smallness of the driving pinion because it must be dimensioned for the output to be transmitted through the input shaft. Moreover there is not much chance of altering the axle offset without simultaneously altering the transmission ratio. Thus, taking into consideration all these conditions concerning the axle offset, the ratio and the practical possibilities, should the conditions governing the vehicle and the power source give rise to a desire to alter the axle offset this may not at all be possible.
And the possibility of adapting an existing transmission to various motor vehicles with possibly different axle offsets in the final drive is also very remote.